(1) Field of the Invention:
This invention relates to a continuous casting apparatus, and more particularly to a continuous casting apparatus for the direction production of cast sheets.
(2) Description of the Prior Art:
Heretofore, metal sheets have been manufactured by preparing an ingot through an ingot making method, blooming the ingot to produce a slab of 100-300 mm in thickness, roughly rolling the slab to obtain a sheet bar of about 30 mm in thickness, and then rolling the sheet bar with a hot strip mill to produce a metal sheet of not more than 10 mm in thickness.
On the other hand, there is a technique for directly producing a cast sheet according to the continuous casting method as shown in FIG. 1. In this technique, molten metal is poured into a water-cooled mold 102 through a nozzle 101, and after a solidification shell 103 is produced along the mold wall, it is continuously drawn from the mold by means of guide rolls 104 and so on in the form of thick cast slab and then roughly rolled into a cast sheet. However, this method has the following defects. That is, according to this method, since the thickness of the cast slab is determined by the diameter of the nozzle 101, it is better to make the diameter of the nozzle smaller. To the contrary, the diameter of the nozzle is necessary to be not less than 100 mm in order to prevent the solidification of molten metal inside the nozzle during the pouring and is usually 150-170 mm. Therefore, the thickness of the castable slab is restricted to about 130 mm at minimun. In this sense, it is a common practice in the conventional technique using the continuous casting method that a mold is designed in a substantially hollow rectangular shape restricted by the diameter of the nozzle as shown in FIG. 1 and is difficult to draw a thinner cast sheet.
Further, there have hitherto been proposed a continuous casting machine for the production of a thinner cast sheet as shown in FIG. 2. In this case, a casting space 108 having a sectional shape and a predetermined length, which correspond to the intended cast sheet, is defined by a pair of endlessly movable metal belts 106 oppositely faced with each other at a given interval and a pair of side plates 107 positioned near the side edge portions of these metal belts. Each of the metal belts is guided and supported along a predetermined running path through guide rolls 110-113, or 110'-113' and cooled by spraying a cooling fluid onto the back side of each metal belt from spray nozzles 115 located between the guide rolls and behind the belt. Thus, molten steel is poured into an upper basin of the casting space from a pouring nozzle 101, and after a solidification shell is produced along the metal belt constituting the casting space, the resulting cast sheet is drawn from the casting space through lower guide rolls 116. According to such a conventional continuous casting machine, for instance, in order to directly obtain a cast steel sheet by the continuous casting method, the interval between the metal belts 106 and 106 is gradually reduced downward from the upper basin of the casting space positioning the end of the nozzle to form a tapered end portion at the lower end of the casting space, which corresponds to the desired thickness of the cast sheet, by means of guide rolls 111, 111'.
In general, the steel sheet is continuously cast at a high speed, so that it is necessary to complete the solidification of molten metal until it passes through the guide rolls 111, 111' positioned at the tapered end portion or to arrange a cooling means immediately beneath the guide rolls 111, 111' for the purpose of restraining the bulging of the unsolidified cast sheet.
In the conventional continuous casting apparatus of FIG. 2, a sufficient amount of the cooling fluid is required to be sprayed onto the metal belts 106 between the guide rolls 110, 111 (110', 111') from the spray nozzle 115 in order to completely solidify molten steel until it reaches the lower end of the casting space. For this purpose, it is necessary to spray the cooling fluid at a spray pressure as high as several tens atmospheric pressure. However, if the cooling fluid of such a high pressure is sprayed onto the metal belt 106, the metal belt may be locally deformed, and in the worst case, the metal belt is broken depending upon the belt material. As a result, the surface of the metal belt becomes uneven, which causes a problem of deteriorating surface properties of the cast sheet 103. On the other hand, when the metal belts 106 beneath the guide rolls 111, 111' are cooled with the cooling fluid sprayed from the spray nozzles 115 to prevent the bulging, since there inherently exists some gap at the lower region of each of the rolls due to the structure of the apparatus, the cast sheet is not uniformly cooled at a place facing this gap. Consequently, uneven cooling takes place to adversely affect the surface properties of the cast steel sheet.
For this reason, it has been proposed to define the casting space with a pair of water-cooled casting wheels instead of the guide rolls. However, since the cooling zone contributing to the completion of the solidification of molten metal is not larger than one-fourth the whole circumferential length of the wheel, it is necessary to enlarge the radius of the casting wheel, resulting in the unfavorable enlargement of the continuous casting apparatus. Moreover, since gaps are also formed just beneath the casting wheels, the same defects as previously described naturally occur.